Does hydroxychloroquine block the ability of coronavirus to interfere with hemoglobin function and preserve its oxygen-carrying capacity in a way that parallels its ability to protect hemoglobin from malaria parasites?

This is very much the case and is an additional indication supporting its use in COVID‑19 pandemic victims. This is exactly what the doctor ordered, something that has molecular specificity for the nature of the damage being produced by the invading virus at the earliest stage in the sequence of events as possible. It is always easier to prevent something like tissue injury than to heal the injury once it has occurred. That is why such agents have an important place as early in the course of the infection as possible because they will do the most good and have the highest impact when given even prophylactically and certainly at the earliest sign of illness because all along the way they will be protecting the host through multiple modes of action and will be reducing the severity of each stage of difficulty that can be encountered. They will prevent people from becoming symptomatic altogether in some instances. They will reduce the need for hospitalization of many who become infected so they only suffer mild symptoms and never get into serious trouble. They will reduce the need for lifesaving measures such as ventilators by keeping the severity within a more manageable range and they will reduce mortality in those who nonetheless develop severe symptoms and are struggling to hang on.